Dynamic tag estimation for optimizing tree slotted aloha in RFID networks

Abstract

The emergent commercial use of techniques for Radio Frequency-based IDentification of different items (RFID) requires the investigation and testing of collision resolution mechanisms for the efficient and correct communication between the system reader and the tags labeling the items that need to be identified. Several MAC protocols have been proposed to resolve collisions in RFID networks. A recent solution, named Tree Slotted Aloha (TSA), has been shown to outperform previous ones with respect to the time it takes for identifying all tags, and the total number of bits transmitted to complete the identification process. However, almost half of the time needed by TSA for identifying tags is spent in collisions. This depends on TSA operation and in particular on the way TSA estimates the number of colliding tags. We have observed that in the case of realistically large networks, TSA highly underestimates this number, with non-negligible impact on the protocol performance. In this paper, we propose a Dynamic Tree Slotted Aloha (Dy-TSA) protocol that exploits the knowledge acquired during ongoing readings to refine the estimation of the number of colliding tags. In so doing, Dy-TSA adapts the length of the following reading cycles to the actual number of tags still requiring identification. Through ns2-based simulations we show that the proposed method is effective for tag identification and results in significantly improved performance over TSA. Specifically, the length of the identification process is up to 20% lower than that of TSA. Furthermore, the amount of transmitted bits needed for identifying all tags decreases up to 30%. Copyright 2008 ACM

Binary Tree Slotted ALOHA for Passive RFID Tag Anticollision

“…The advantages of the three propose protocols are to require no estimation of the number of tags, and their efficiencies are not affected by the variance of the number of tags. Their efficiency is not only higher than the existing protocols without estimation, but also close to and even higher than the TSA-based protocols with estimation [11], [12], [13].…”

“…Compared with fixed framed slotted ALOHA, Dynamic FSA can achieve a higher efficiency value of 0.37. To improve the identification efficiency, someone integrates tree algorithms into ALOHA-based protocols, and proposes several hybrid protocols: TSA protocol [11], dynamic TSA protocol (DyTSA) [12], binary splitting TSA (BSTSA) protocol [13], adaptive splitting-based arbitration protocol (ASAP) [24] and a hybrid protocol in [30], where tree algorithms resolve a collision by successively muting subsets of tags that are involved in the collision [14], [15]. The hybrid protocols can achieve higher efficiency than Dynamic FSA.…”

“…If some tags collide in a slot, the collided tags in the slot will be resolved by binary tree (BinTree) splitting at once while the other tags in the subsequent slots will wait. When an initial frame length, i.e., the slot number in an initial frame is equal to the number of tags, BTSA can achieve a maximum efficiency value of about 0.43 [14], which is higher than the efficiency of dynamic frame slotted ALOHA (Dynamic FSA) [6], [7], [8], [9], [10] protocol and pure binary tree protocol [15], and nearly equal to the ideal tree slotted ALOHA (TSA) protocol's [11], [12], [13] optimal efficiency. In order to obtain the maximum efficiency, the initial frame length should be set according to the number of tags which is, however, usually unknown to a reader.…”

Anonymous Cardinality Estimation in RFID Systems with Multiple Readers

“…3 shows the percentage of error in approximating the variance of the estimation error versus the load factor. The y-axis is |(σ 2 −σ 2 )|/σ 2 × 100%, where σ 2 is the actual variance of the estimator error obtained via simulation and σ 2 is the approximated value from (12). Results show that the approximation error decreases when the persistent probability p reduces.…”

“…Given the number of empty slots and slots with single and collision transmissions in a framed-slotted ALOHA model, the number of tags is estimated as the value which maximizes the a posteriori probability. Other tag estimation techniques have also been proposed in the literature for RFID systems with a single reader [12], [13].…”